Beverage flasks are normally made from glass and have a curved shape that facilitates carrying adjacent the body within a clothing pocket or otherwise. Such flasks are conventionally made from glass which can break if dropped or struck sharply. Also, glass flasks are relatively heavy which results in a weight disadvantage in addition to the breakage problem.
Plastic flasks have previously been developed to eliminate the breakage and weight problems involved with glass flasks. However, the walls of plastic flasks are substantially thinner than glass flasks which results in a packaging problem in relationship to the size of plastic flasks. A plastic flask that holds a given volume of liquid beverage necessarily has a much smaller outer size than a glass flask as a result of the thinner wall thickness of the plastic flask. This is a disadvantage from a marketing standpoint in that the consumer upon viewing glass and plastic flasks side-by-side will erroneously assume that tha plastic flask contains less liquid beverage. Furthermore, filling operations, packaging, shipping and store shelving considerations also make it desirable for a plastic flask to have the same height and lateral width as a glass flask for holding the same amount of liquid contents.
Injection stretch blow molding has previously been utilized to provide plastic containers whose mechanical properties are improved as a result of biaxial orientation that results from the stretch blow molding process. Such injection stretch blow molding has previously been done with round containers made of polyethylene terephthalate as disclosed by the U.S. Pat. No. 3,733,309 of Wyeth et al.